Electron-discharge device



ELECTRON DISCHARGE DEVICE Filed Sept. 5, 1925 Patented den. 22, ldltll.

stares SOLOMON BBESSLER, F BROOKLYN, NEW YORK.

ELECTROIl -DISGI-IARGE DEVICE.

Application filed September 3,1925. Serial m. 54,369.

The invention relates to improvements in the control electrode or grid of said device; and the object of the improvement is an in crease of mutual conductance obtainable with a certainexpenditure oi energy.

In the accompany diagram, Figure I representsa cross-section of a three electrode vacuum tube; (1) is thefilament or cathode, (2) is the grid or electrostatic control electrode, and (3) is the plate or anode. In Figure II, (4) and (5) are cross sections of grid members.

In order that my invention be more clearly understood, I shall briefly state some necessary theoretical explanations.

In 1919, Ballantine pointed out that Van der Bijls theory of action in a three electrode vacuum tube was contrary to results after certain applied potentials were. reached. Since then, there have been many verifications of Ballantines experiments- I have been led to formulate anew theory or action in said tubes, viz: the mutual conductance is a function of the velocity of the electron stream as it passes thru the meshes of the grid structure and the electrostatic capacity between the grid wires and the surrounding electron stream.

The basis of my theory of action is the well known fact, self evident from our knowledge of electron behavior, that in a direct current of electricity thenu nber of elec trons passing any cross-section of the circuit equals the number passing any other crosssection in the same time. I consider the grid plane, a cross-section of the plate circuit.

Let a be the instantaneous number of electrons in the tree spaces between the grid wires, and o their average velocity. Then 1p, the plate current, equals are a being the electron charge. It g be the iuunber of free electrons in the grid wires above or below the electrostatically neutral state; then Q, the total number oi free electrons in the grid plane above the electrostatically neutral state, equals n+q d-a correction factor that may be suggested. In this discussion the filament emission of electrons and the plate circuit voltage are considered constant. Therefore the quantity Q is considered constant. The quantity q depends upon several factors only one of which need be considered, i. e., the electrical capacity eilect between the grid wires and the surrounding electron stream. This etlect arises from the fact that the grid wire surfaces while able to absorb electrons cannot ordinarily emit any into the surrounding field therefore constituting a high resistance between the free electrons in the grid wires and those in the immediate vicinity of the wires. If c be this capacity and E9 i u n the grid voltage, then g equals By diilerentiation we obtain The action in a three electrode vacuum tube may be considered to take place as follows: The conditions under which said tube operates are the unusual constancy of filament electron emission and plate circuit voltage, which voltage is below that necessary tor saturation current. Under these conditions the number of free electrons in the space be tween the filament and the plate is constant. The constancy of this number is self evident, for, it no electrons were absorbed by the plate from the free space, then a point would be reached where as many electrons would return to the filament as were admitted by it. Let a number of electrons be absorbed by the plate, a number less than that emitted by the filament. Then the number returned to the filament would be lessened by the exactnumber absorbed by the plate, and the law Ip=ace will hold. This leaves the number of free electrons in the interelectrode space unchanged. In actual practice, however, ad ditional negative potential on the filament induced when the plate voltage increases, tends to increase the electron emission, therefore increasing the number of electrons in the free-space. In any event the electron condition in the free-space is such that said space may be considered an ordinary electrical conductor. Hence, tube characteristi tend to prove that the resistance of this tree space is inversely proportional to the number oi electrons in said free space. y

A varying voltage on the grid changes the number of free electrons in the grid wires. As this number changes, the number of electrons in the tree spaces immediately surrounding the grid wires changes according to the formula: Q=a+g. Thus it the grid voltage decreases the number of electrons in the grid wires, the number of electrons in the tree spaces of the grid cross-section a will be increased; Since plate current equals noethe plate current increases. In addition, the resistance to the plate current flow in the free space, which is an inverse function of the number of free electrons in said free space lessens, thereby increasing the plate current by increasing the velocity a. When the grid voltage is reversed the opposite eiiect takes place. It must be remembered that When the grid is at such a potential that it absorbs electrons the action is further complicated and the formula given does not hold. To obtain a maximum change in plate current with a definite grid voltage it is necessary to place the grid structure in such a position that the term a n +o 18 at a maximum.

It is evident from the diagram, in Fig. 1, the grid and in Fig. 2 the cross sections (4), (5) of said grid; that my grid structure consists of members With irregular surfaces and irregulz'ir cross sections respectively. These irregularities may take many forms and I do not limit myself to the forms shown in my dia ram. I consider only those grid members WlllCh have surface areas greator than the surface areas of the cylinders that might be circumscribed about their long axes. Expressed differently, the grid memhere may be considered as cylinders from which segments have been removed to such an extent. that the grid members have a reater surface area than the ori inal cyliners. However, the removal of said se ments is affected in such a manner that a l the points at the extremities of the cross-sections of said grid members lie in the surfaces of the said original cylinders. The purposes of this form of segmentation are to prevent an increase in plate resistance and electrostatic capacity etween the grid and other electrodes in the device as hereinafter explained. Thus, by increasing the surface areas, the capacity a is increased.

In my invention, the increase in mutual conductance is obtained by the said increase in the capacity 0 of the equation herein mentioned, so that more electrons enter or leave the grid for the same voltage used, producing a greater change in the term n of the herein aforementioned equation for the same applied grid voltage.

The terms a and o of the equation, heretoforementioned, depend upon the amount of free space in the "rid cross section. The customary methods 0 increasing grid surface area arezthe increase of the number of the grid members or the increase of the size of said grid members. In either case, the free space between the grid members is reduced, thus decreasing the terms a and o.

By employing my forms of grid members no reduction in the free spaces? between the grid members takes place. In fact, by employing some of my forms, it is possible to increase the said free space. Therefore my forms of grid members differ from the usual forms in that they do not reduce the terms a and c.

Having thus clearly shown the nature of my invention, I claim the following:

In an electron discharge device, an electrostatic controlling means in the electron stream, said means constructed of irregular surfaced members, all the points at the extremities of the cross sections of said grid members lying in the surfaces of cylinders that might be circumscribed about the long axes of said grid members, and the surface areas of said grid members being larger than the surface areas of said cylinders.

SOLOMON BRESSLEH. 

